1. Field of the Invention
This invention relates to apparatus for feeding solid fuel to a furnace grate and also relates to a furnace and to a boiler incorporating such an apparatus.
The invention has been developed particularly for incorporation in a shell boiler of the type, hereinafter referred to as the type described, comprising an outer continuous shell within which is contained the steam and/or water space of the boiler, a furnace grate and a plurality of smoke tubes for passage therethrough of the products of combustion of the furnace and the boiler having apparatus for feeding solid fuel to the furnace grate downwardly through the steam and/or water space of the boiler.
Although an apparatus according to the invention has been particularly designed for incorporation in a shell boiler of the type described, the apparatus may be used to feed any other desired furnace grate.
An object of the present invention is to provide a new and improved apparatus for feeding fuel to a furnace grate.
2. Summary of the Invention
According to a first aspect of the present invention we provide an apparatus for feeding solid fuel to a furnace grate comprising a conduit adapted, in use, to extend downwards through the roof of the furnace, means for feeding solid fuel to the conduit above the lower end thereof said means including at least one fuel propulsion element and drive means to cause the element to move to propel the fuel in a desired direction and means to cause a rapid deceleration in the movement of the element whereby any fuel adhering to the element is flung therefrom.
Preferably the element is mounted on a driven shaft for rotary movement about an axis, at least part of the element being resiliently mounted relative to the shaft and said part of the element being engageable with an abutment whereby on rotation of the shaft said part of the element is prevented, temporarily, from rotation to cause movement of said part relative to the shaft against the resilient bias so that upon release of said part from the abutment said part is rapidly accelerated and then decelerated to return it to its normal orientation relative to the shaft, thus providing a "flick" action whereby any fuel adhering to the element is flung from the element.
Preferably, the element is inherently resiliently deformable whereby said resilient bias is provided.
A plurality of elements may be mounted on such shaft at spaced angular positions.
The shaft may be mounted for rotation about a horizontal axis and the fuel may be fed thereto at an angle inclined to the vertical whereby the element or elements act to propel the fuel in a direction so that it is turned from its direction of feed into the vertically downwardly extending conduit.
Normally the fuel is fed to the element in a horizontal direction.
The apparatus may include a pneumatic fuel feed pipe extending from a source of fuel supply towards the conduit along which fuel is fed by air under pressure and a vent means whereby the pneumatic feed air is vented from the fuel feed pipe at a position adjacent to and upstream of the position of connection between the fuel feed pipe and the conduit.
According to a second aspect of the present invention we provide a boiler of the type described incorporating a fuel feed apparatus according to a first aspect of the invention.
The boiler may be provided with means to extract fuel dust entrapped in the vented air from the vented air and to feed the fuel dust into the furnace of the boiler.
Preferably, when the boiler has a grit arrestor arranged to extract grit entrained in the exhaust gas of the boiler and a means to return the extracted grit to the furnace, the vented air is fed to the grit arrestor whereby the fuel dust is extracted from the air and returned to the furnace.
By venting the pneumatic feed air before entry into the downwardly extending conduit, the speed at which the fuel enters the conduit is reduced thereby reducing breakage of the fuel and so reducing the amount of very fine fuel entering the furnace.
In addition, it may be that the quantity of air introduced into the furnace through the feeding apparatus is too great a quantity for the desired conditions of combustion and hence venting of the pneumatic feed air avoids this problem.
A further problem is that the air in the pneumatic feeding arrangement normally contains a relatively large amount of fine fuel dust, if this fuel dust enters the furnace through the downwardly extending conduit there is a substantial chance that the dust will immediately leave the furnace along with the products of combustion as the dust enters the furnace in relatively close proximity to the outlet thereof.
By venting the pneumatic feed air a large proportion of this dust is also vented and is preferably, as mentioned hereinbefore, reintroduced into the furnace.
The boiler may have, in use, an internal pressure greater than the ambient pressure and there being a conduit extending from the combustion chamber of the furnace whereby the atmosphere in the furnace, and entrained grit, may be vented from the furnace.
The conduit may lead to a grit collection hopper or to a pneumatic grit transport system. In the latter case the pneumatic grit transport system may transport the grit to a conventional grit arrestor and thereafter the grit may be reintroduced into the furnace.
By feeding grit laden air from the furnace, as described hereinbefore, the amount of grit in the flue gases leaving the furnace is considerably reduced or completely eliminated thus avoiding the problems which are conventionally incurred due to grit laden flue gases.